Method of making integrally finned metal tubing



May 28, 1968 B. R. WARD, JR

METHOD OF MAKING INTEGRALLY FINNED METAL TUBING 2 Sheets-Sheet 1 FiledApril 27, 1965 INVENTOR BENNIE RWARQJR.

y 8, 1968 a. R. WARD, JR 3,384,946

United States Patent 3,384,946 METHOD OF MAKING INTEGRALLY FINNED METALTUBING Bennie R. Ward, Jr., Chesterfield County, Va., assignor toReynolds Metals Company, Richmond, Va., a corporation of Delaware FiledApr. 27, 1965, Ser. No. 451,273 2 Claims. (Cl. 29157.3)

ABSTRACT OF THE DISCLOSURE integrally finned metal tubing is made by aprocess of roll-welding metal sheets by passing them between rollerswhich act against a mandrel to deform, elongate and bond the sheetstogether in the configuration desired for said tubing.

This invention relates to integrally finned metal tubes and the like andto methods of making the same.

It is well known that many different types of heat exchangers utilizehollow tubes through which a cooling or heating medium is circulated,whereby the outer peripheral wall of the hollow member forms the primaryheat exchange surface for heat transfer purposes. Examples of such heatexchangers are automobile radiators and convectors for space heating.

In order to increase the heat transfer between the primary and secondaryheat exchange mediums, various manufacturers increase heat transfer areaby providing fins in contact with the outer surface of the tubes. Suchcontact must be intimate if the fins are to serve their purposeefficiently. Various systems have been devised for mechanicallyconnecting the fins to the tubes. Other systems connect the two by anintermediate material, as by tinning, welding, soldering, brazing, andthe like. Still other systems utilize fins which are integral with thetubes, thereby efiiciently providing continuous and uninterrupted heatflow paths.

The present invention concerns tubes of this latter type, and, moreover,methods for economically and conveniently producing the same. The tubesaccording to the invention have external radial fins integral with thebody of the tube, and may be conveniently produced directly for flatmetal strip or sheet in a single operation. For some applications, forexample where a relatively corrosive heat exchange fluid will passthrough the interior of the tube, it may be desirable to provide a tubelining of a different material. In accordance with the invention, suchcomposite tubes may be conveniently produced directly from fiat metalstrip or sheet, and metal tubing, in a single operation.

The heat transfer characteristics of the tube according to the inventionmay be enhanced by deforming the integral fins in accordance with theassignees copending application Ser. No. 332,818 by Loehlein and Curran.

For a better understanding of the invention, and of its other details,objects, and advantages, reference is now made to the accompanyingdrawings, which show, for purposes of illustration only, a preferredembodiment of the invention. In the drawings:

FIG. 1 is a semi-diagrammatic sectional elevation view of suitableapparatus carrying out and producing the invention;

FIG. 2 is a sectional view taken at II-II in FIG. 1;

FIG. 3 is a semi-diagrammatic sectional elevation view of suitableapparatus carrying out and producing an alternate form of the invention;

FIG. 4 is a sectional view taken at IV-IV in FIG. 3;

FIG. 5 is a sectional view of another alternate form of the invention;and

FIG. 6 is a traverse view of still another alternate form of theinvention.

Referring now more particularly to the drawing, when composite finnedtube is to be produced, mandrel 10 having a tip 16 of circularcross-section is inserted through pre-heated copper or aluminum tube 12.The rearward end of mandrel 10 is anchored to stationary member 14 sothat tip 16 extends into circular, circumferential grooves 18 in rolls20. Aluminum sheets or strips 22 are wound off storage coils (not shown)thru a pre-heating station (not shown) and are inserted between the nipsof rolls 20 at opposite sides of mandrel tip 16 and tube 12. Rolls 20then rotate in direction 24, thereby: pulling tube 12 and strips 22through the roll pass; deforming and elongating tube 12 into tube 13 ofreduced thickness; deforming and elongating strips 22 intoconfigurations of reduced thickness having grooved portions 23 and flatportions 25; bonding grooved portions 23 to tube 13; and bonding fiatportions 25 together to form fins 26. The inner diameter of tube 12 isunchanged.

It can be seen that the circumference of the roll surface varies acrossgroove 18, so that for each revolution of roll 20' the metal contactingthe deepest portion of groove 18 tends to move forward (in the directionof rolling) at a lower speed than the metal in fins 26 and the metal inthe shallower portions of groove 18. This effect tends to cause thebonded sheets 23 to tear apart instead of normally leaving the area ofcontact with rolls 20, or at least to slip with respect to the surfacesof grooves 18. In the embodiment described above, however, this has notbeen found a problem, probably because of the strong bond betweengrooved portions 23 and tube 13, as well as between flat portions 25.

The composite finned tube is not necessary for a large number ofapplications. In the alternate form of the invention shown in FIGURES 3and 4, inner tube 12 has been omitted, so that strips 22 directlycontact and defor-m around mandrel tip 16. In the resultant product,grooved portions 23' define the internal passage and fiat portions 25are bonded together to form fins 26'. By omitting tube 12, this form ofthe invention is suitable for a continuous operation.

In contrast to mandrel tip 16 of circular cross-section, mandrel tip 16is of oval or elliptical cross-section, being oriented with its majordiameter perpendicular to the axes of rotation of rolls 20. Grooves 18continue to have a cross-section defined by an arc of a circle. Thisdesign, by causing the thickness of grooved portion 23 to be a minimumat the plane perpendicular to fins 26' and a maximum adjacent fins 26,eliminates the tendency of the bonded sheets to tear apart or slip withrespect to the surfaces of grooves 18. Instead, the variation in metalthickness equalizes the variation of the linearly translated speeds ofthe surfaces of groove 18, thereby promoting uniform metal flow in thedirection of rolling throughout grooved portion 23'.

In another alternate form of the invention shown in FIGURE 5, mandreltip 30 and .grooves 32 in rolls 34 are of a partially rounded rhombiccross-section, so that in the resultant product, grooved portions 36define the internal passage and flat portions 38 are bonded together toform fins 40. The thickness of the grooved portions 36 and fiat portions38 is uniform in the direction perpendicular to the axis of rotation ofrolls 34. The walls of grooved portions 36 meet at at angle along lines42 where the bond between flat portions 38 is exposed to the tubepassage. Like the finned tube shown in FIGURES 3 and 4, this finned tubeis suitable for a continuous operation. Where ultimate heat exchange andfluid flow considerations permit, there are certain advantages to themodified rhombic cross-section. First, the bonds along lines 42 3 aresmooth and complete. Further, the same mandrel tip 30 and rolls 34 canbe used for different roll settings and sheet thicknesses.

It will be clear that by providing a roll with a number of spacedcircumferential grooves and using with each such groove a mandrel havinga complementary shape, relatively wide sheets can be deformed,elongated, and bonded into a heat exchange panel having multiplepassages and fins. Each such panel will constitute, in effect, aplurality of finned tubes sharing common integral fins. In thisconnection, FIGURE 6 shows an exemplary heat exchange panel having aplurality of partially flattened rhombic passages 50 and fins 52.

The invention is further illustrated in the following examples:

Example 1 Two directly-driven rolls were set .025 inch apart. Each rollhad an 8 inch width, a inch diameter, and a inch substantiallysemi-circular, circumferential groove at the center of its width. The A1inch diameter mandrel was coated with graphite grease. Two annealed 5457aluminum alloy sheets having a thickness of .040 inch and a width of 6inches were wire brushed on one surface. An annealed 6063 aluminum alloytube having a A inch LB. and a inch O.D. was belt sanded to remove thelayer of surface oxide. The tube was disposed between the wire-brushedsurfaces of the two sheets and the sandwich preheated at 1000 F. forfive minutes. The forward end of the mandrel was inserted through thetube of the preheated sandwich. The rear end of the Example 2 Theprocess of Example 1 was carried out with the inner tube being made ofcopper rather than 6063 aluminum alloy. The substitution of materialsdid not significantly alter the process or the resultant product.

Example 3 The process of Example 1 was carried out with two 1100aluminum alloy sheets of .060 inch thickness being substituted for each.040 inch thick aluminum sheet. The resultant composite productexhibited good bonds between the tube and sheet and between the sheetitself. The fin thickness was .063 inch.

It will be apparent that in practicing the invention variousmodifications can be made in the embodiments described above: The rollsurfaces can be lubricated by spraying the inner surfaces of the fiatsheet. Instead of the two cylindrical rolls shown, three or moreTurks-head rolls can be employed, thereby to form a corresponding numberof fins. Initially the inside edges of the metal strips can be coatedwith a stop-weld material, so that following the deforming and bondingoperation the tips of the fins can be deformed away from the plane ofthe bonded portions of the fins, thereby to provide increased heattransfer area. When a composite tube is desired, a plurality of metalsheets can be passed on each side of the mandrel in the operation shownin FIGURE 3. The shape of the grooves in the rolls and the shape of themandrel can be changed to produce tubes of various cross-sectionalshapes other than circular, oval, or modified rhombic.

While present preferred embodiments of the invention, and methods ofproducing the same, have been illustrated and described, it will berecognized that the invention may be otherwise variously embodied andpracticed within the scope of the following claims.

What is claimed is:

1. A process of roll welding to form a composite finned tube, comprisingpreheating a plurality of malleable metal sheets, passing said sheetssimultaneously into contact with a mandrel positioned therebetween andthrough rolls adjacent said mandrel, said rolls having a circumferentialgroove aligned with said mandrel and of a shape generally complementingsaid mandrel, so that first portions of the sheets contact said mandreland deform into said grooves so as to enclose a generally tubular space,said deformation causing substantial elongation and reduction inthickness across the entire said first portions, and so that secondportions are urged together by said rolls and are thereby reduced inthickness, elongated to substantially the same extent as said firstportions, and roll-welded to form fins extending radially outward fromsaid first portions.

2. The process of claim 1 wherein an inner surface of a said metal sheetis coated adjacent its edge with a stopweld material, and following saiddeforming and said welding of said sheets the edges thereof areseparated and deformed to increase the heat transfer area of said fins.

References Cited UNITED STATES PATENTS 3,123,905 3/1964 Thomas 29475 X3,145,456 8/1964 Johnson 29157.3 3,178,806 4/1965 Keith 29--157.33,220,106 11/1965 Clark 294975 3,220,107 11/1965 Clark 29497.5

FOREIGN PATENTS 485,801 11/1929 Germany.

CHARLIE T. MOON, Primary Examiner.

P. M. COHEN, Assistant Examiner.

